With the development of consumer electronic audio/video (A/V) equipment, and the advance of digital A/V applications, such as consumer A/V device control and signal routing and home networking, various types of data in various formats can now be transferred among several audio/video control (AV/C) devices via one digital bus system. However, many current systems do not have sufficient bandwidth resources to transfer and display all the different types of data at the same time.
Typical computer systems solve the bandwidth problem by increasing the bandwidth of the system bus to handle all of these forms, types and amount of data. As a result, as users request more types of information such as in multimedia applications, the system bus has become more clogged with information other than information directly utilized and needed by the main processor.
Many computer systems incorporate at least two buses. A first bus, commonly referred to as a memory bus, is typically used for communications between a central processor and a main memory. A second bus, known as a peripheral bus, is used for communications between peripheral devices such as graphics systems, disk drives, or local area networks. To allow data transfers between these two buses, a bus bridge is utilized to “bridge” and thereby couple, the two buses together.
One example of a high-speed bus system for interconnecting A/V nodes, configured as a digital interface used to transport commands and data among interconnecting audio/video control (AV/C) devices, is the IEEE 1394 standard serial bus implemented by IEEE Std 1394-1995, Standard For A High Performance Serial Bus, Aug. 30, 1996 (hereinafter “IEEE 1394 standard”) and related other 1394 standards.
The IEEE 1394 standard is an international standard for implementing a high-speed serial bus architecture, which supports both asynchronous and isochronous format data transfers. The IEEE 1394 standard defines a bus as a non-cyclic interconnect, consisting of bus bridges and nodes. Within a non-cyclic interconnect, devices may not be connected together so as to create loops. Within the non-cyclic interconnect, each node contains an AV/C device, and bus bridges serve to connect buses of similar or different types.
The primary task of a bridge is to allow data to be transferred on each bus independently without demonstrating performance of the bus, except when traffic crosses the bus bridge to reach the desired destination on the other bus. To perform this function, the bridge is configured to understand and participate in the bus protocol of each of the buses.
Multi-bus systems are known to handle the large amounts of information being utilized. However, communication between buses and devices on different buses is difficult. Typically, a bus bridge may be used to interface I/O buses to the system's high-performance processor/memory bus. With such I/O bridges, the CPU may use a 4-byte read and write transaction to initiate DMA transfers. When activated, the DMA of a serial bus node generates split-response read and write transactions which are forwarded to the intermediate system backbone bus which also implements serial bus services.
Depending on the host system design, the host-adapter bridge may have additional features mandated by differences in bus protocols. For example, the host bus may not directly support isochronous data transfers. Also, the host-adapter bridge may enforce security by checking and translating bridge-bound transaction addresses and may often convert uncached I/O transactions into cache-coherent host-bus transaction sequences.
Each time a new device or node is connected or disconnected from an IEEE 1394 Standard Serial Bus, the entire bus is reset and its topology is reconfigured. The IEEE 1394 Standard Device Configuration occurs locally on the bus without the intervention of a host processor. In the reset process, three primary procedures are typically performed; bus initialization, tree identification, and self-identification. Within the IEEE 1394 Standard, a single node must first be established as the root node during the tree identification process in order for the reconfiguration to occur.
A conventional isochronous bus connection includes multiple buses, one or more bus bridges, a talker node, and one or more listener nodes. A talker node usually provides an isochronous data stream and forwards the isochronous data stream onto a bus. A listener node typically reads the packets from the isochronous data stream.
A typical method for establishing communication between the talker node and the listener node is to build isochronous bus connections from the talker node toward the listener node.
A problem with the maintenance communication between the talker node and the listener node is that when busIDs have changed, nodes need to be notified of this occurrence. Another problem associated with the maintenance isochronous stream is notifying listeners when isochronous bandwidth requirements have changed. One approach to notifying nodes of bandwidth changes in the talker is to initiate a broadcast event that would inform other nodes of the bandwidth-requirement change. However, this approach is complicated and unnecessarily signals uninvolved controllers.